Methods and materials for treating investment casting patterns

ABSTRACT

Investment casting patterns are treated with a liquid mixture consisting essentially of an aqueous dispersion of colloidal refractory particles and a medium comprising a watersoluble organic liquid in order to render the pattern surfaces hydrophilic and thereby promote uniform surface coverage by water-base refractory slurries used in the production of ceramic shell molds and bulk investment molds.

,1 o r, i 1, l-1 Unite tts tent 1191 1111 3,836,372 Horton Sept. 17,1974 [54] METHUDS AND MATERIALS FOR 2,842,445 7/1958 Emblem 106/3835TREA'HNG INVESTMENT CASTING 3,258,348 6/1966 Reuter 106/3835 3,270,3829/1966 Emblem et a1. 106/383 PATTERNS 3,326,269 6/1967 Schneider 106/383[75] lnventor: Robert A. Horton, Chesterland, 3,399,067 8/1968 Scott106/383 Ohio 3,748,157 7/1973 Moore 106/383 3,754,946 8/1973 Moore106/383 [73] Assrgnee: Precision Metalsmith, Inc.,

Cleveland, Ohlo Primary Examiner-Lorenzo B. Hayes [22] Filed: May 5 1972Attorney, Agent, or Firm-Watts, l-loffmann, Fisher &

Heinke Co. [21] Appl. No.: 253,177

[57] ABSTRACT [52] US. Cl 106/3822, 106/3827, 106/383, Investmentcasting patterns are treated with a liquid 106/3 8.35, 106/389 mixtureconsisting essentially of an aqueous dispersion [51] lint. (I1 B28b 7/36of colloidal refractory particles and a medium com- [58] Field of Search106/383, 38.35, 389, prising a watersoluble organic liquid in order torender 106/3822, 38.27; 164/25, 26 the pattern surfaces hydrophilic andthereby promote uniform surface coverage by water-base refractory [56]References Cited slurries used in the production of ceramic shell moldsUNITED STATES PATENTS and bulk investment molds.

2,380,945 8/1945 Collins 106/383 15 Claims, N0 Drawings METHODS ANDMATERIALS FOR TREATING INVESTMENT CASTING PATTERNS BACKGROUND OF THEINVENTION The present invention relates generally to the investmentcasting art, and more specifically to methods and materials for treatinginvestment casting patterns to promote uniform surface coverage of thepatterns by' water-base refractory slurries used in the production ofceramic shell molds and bulk investment molds.

As is known to those familiar with the art of investment casting,ceramic shell molds and bulk investment molds are made using disposablepatterns which typically are composed of organic material, such as wax,synthetic resin, or a wax and synthetic or natural resin composition.The patterns are surrounded with refractory slurry which is allowed toharden, the patterns being subsequently destroyed to form the moldcavities. Bulk investment molds are produced by dipping an assembly ofpatterns in refractory slurry, sanding the coated patterns while wetwith coarse refractory particles, and drying the coating to form a thin,hard layer. After this dipcoat or pre-coat has dried, the patternassembly is placed in a flask and the flask is filled with acementitious refractory material known as investment which hardens toform the bulk of the mold. In some instances, as when using aplaster-base investment, the dip coat or pre-coat can be omitted.Ceramic shell molds are usually prepared by forming a plurality ofhardened refractory layers around a pattern assembly in the same manneras the dipcoat in the production of bulk investment molds. The steps ofdipping, sanding and drying are repeated until a refractory shell of thedesired thickness has been built up around the pattern assembly.

A problem encountered in the production of both types of investmentmolds described above is that of the refractory slurry failing to wetthe surfaces of the patterns, as is necessary to obtain uniform patterncoverage and to form a dense, void-free mold face capable of reproducingthe pattern detail. In extreme situations where the slurry does not havethe ability to wet the patterns at all, most of the slurry will run offthe patterns when they are withdrawn from the slurry bath so that thepattern surfaces are substantially bare. In less severe cases, theslurry coating gradually withdraws or recedes from some areas of thepattern surfaces, a condition referred to as dewetting. Although grosswithdrawal or dewetting can be alleviated to some extent by sanding orstuccoing the slurry coating immediately after the dipping operation,localized dewetting may still occur throughout the coating so thatcastings made in the molds have a condition of overall surfaceroughness.

The most common condition encountered in the production of shell moldsis that the slurry, while appearing to coat the patterns satisfactorily,does not actually wet difficult areas, such as tiny holes, narrow slots,serrations, sharp corners, etc. Castings made by use of such improperlycoated patterns exhibit characteristic defects such as small globules ofmetal corresponding to air bubbles which the slurry did not displacefrom the pattern and indistinct detail in areas where the slurry coveredover a negative feature in the pattern surface instead of penetratinginto it. The same types of problems encountered in forming ceramic shellmolds also may be encountered in forming bulk investment molds. This isparticularly true when a precoat is applied to the patterns beforeinvesting, since the precoat operation is identical to that of applyingthe first slurry coating in shell forming operations. When the precoatis eliminated and the investment is poured directly around the patterns,failure of the investment slurry adequately to wet the patterns canresult in an inability of the slurry to displace air bubbles and afailure to penetrate fine detail of the patterns, etc.

The wetting problem is of particular significance because of theextensive use of water-base slurries, i.e., slurries formulated withaqueous binders, in the investment casting industry. This is due to thefact that the organic pattern materials commonly employed in investmentcasting processes, including jewelry and dental casting, are not readilywetted by water. In spite of the wetting problems attendant to the useof aqueous binders, such binders are widely used in formulating dipcoatslurries and investments for a number of reasons. Water-base binders donot present the fume and fire hazards accompanying the use ofsolventbase systems, e.g. ethyl silicate-alcohol systems. In addition,aqueous binders are economical and readily available. Aqueous colloidalsilica sols, for example, are frequently employed in formulatingwater-base slurries for ceramic shell operations and for precoatslurries used in making bulk investment molds. Aqueous colloidalsilica-type slurries are often used for the first slurry coating whichis applied directly to the patterns even in systems relying primarilyupon ethyl silicate as a binder for subsequently applied coatings.Aqueous slurries based on sodium silicate as a binder also are used forceramic shell mold operations and precoats for investment operations.Slurries used as the investment in making bulk investment molds containsuch binders as gypsum plaster, metallic phosphates, calcium aluminate,sodium silicate, colloidal silica and others.

It has been conventional to add wetting agents to water-base slurries inattempts to improve the ability of the slurries to wet organic patterns.Typical wetting agents which have been used include sodium dioctylsulfosuccinate, various polyoxyethylene ethers and complex phosphateesters. Many of these wetting agents are not completely compatible withthe slurries and cause localized gelling if added improperly. Even whenproperly added, the agents can cause a gradual thickening of the slurry.Furthermore, the use of wetting agents generally promotes the formationof air bubbles in the slurry and foam on the top of the slurry bath. Insome instances, lower shell strengths result when particular wettingagents are used, and this may be due to the formation of air bubbles andthickening of the slurry. Among other disadvantages, it has been foundthat certain wetting agents lose their effectiveness with time afterhaving been added to the slurry baths. This makes it necessary tomonitor the slurries after they have been formulated and to add freshquantities of the wetting agent at periodic intervals.

Recently it has been suggested that the wetting problem could bealleviated by coating disposable patterns with fumed silica particles.Fumed silica is a submicroscopic pyrogenic silica made by the vaporphase hydrolysis of silicon tetrachloride at a temperature of about1100C. Because of their elevated temperature origin, fumed silicas arecharacterized by having the sil' ica particles sintered together inchain-like formations having a branched structure. In practice, thefumed silica is suspended in alcohol and applied to the pattern surfacesby dipping. After the suspension has dried, the pattern surfaces arehydrophilic and can be wetted by aqueous slurries.

While the use of fumed silica in the manner described represents asignificant improvement over the use of wetting agents, there aredistinct disadvantages which limit its usefulness. Fumed silica is of anextremely fine, light powdery consistency so that it is difficult tohandle during weighing and mixing. High shear mixing equipment which isnot readily available in investment casting foundries is required todispense fumed silica in the liquid medium. Even when such equipment isavailable, it is difficult to obtain a stable dispersion or suspensionso that settling often occurs during transit, in storage and in use.This requires that the mixture be constantly restirred. Also, due to thefact that fumed silica has a chain-like structure as distinguished frombeing discrete particles, it tends to form a network structure whendispersed in the liquid medium which results in a strong thickeningeffect. Consequently, the viscosity of the dispersion is sensitive toconcentration and undue thickening can occur simply because ofevaporation of the medium. This necessitates that the dispersion bemonitored in use and that additional quantities of the medium be addedas it is required.

SUMMARY OF THE INVENTION The present invention provides for thetreatment of disposable investment casting patterns composed primarilyof organic material by a process and with a liquid mixture which iseffective to render the pattern surfaces hydrophilic. Patterns renderedhydrophillic by being processed according to the invention are readilywetted by water-base slurries used in the production of bulk investmentmolds and ceramic shell molds, whereby uniform coverage of the patterns,including penetration of the slurry into all of the intricate surfacedetail, is obtained. 7

The new pattern treating liquid mixture provided by the inventionconsists essentially of discrete colloidal refractory particlesdispersed in a liquid medium which at least in part includes an organicliquid characterized by the capability of wetting the pattern, thecolloidal refractory being present in the mixture in an amount of atleast about 0.5 percent by weight and the organic liquid being presentin an amount sufficient to cause the mixture to wet the pattern.Preferably, the organic liquid is included in an amount exceeding about6 percent by weight of the mixture. In more specifically preferredembodiments, the liquid mixture is formulated by mixing an acidic,aqueous sol of colloidal refractory particles with at least one organicliquid characterized by being soluble in water in all proportions and bya surface tension value of less than 28 dynes per centimeter at C. Themost preferred organic liquids have a surface tension of less than 24dynes per centimeter at 20C. and are more volatile than water. Inaccordance with the preferred method of the invention, a disposableorganic pattern is coated with the liquid mixture, as by dipping, and isthen dried to deposit the colloidal refractory particles on the patternsurfaces and thereby render the pattern surfaces hydrophilic.

Since the new mixture is formulated with liquids, the problemsassociated with the handling of extremely dusty materials such as fumedsilica are eliminated. The liquids are easily mixed together with littleor no agitation so that special high shear mixing equipment and the likeis not required.

As distinguished from the network structure formed by fumed silica whendispersed in a liquid medium, the mixture of the present invention ischaracterized by a dispersion of discrete colloidal refractoryparticles. These discrete refractory particles do not have the samethickening tendency as fumed silica and the liquid mixture maintains ausable viscosity over a wide range of refractory concentration. As aresult, the effect of evaporation on viscosity is minimal so that thereis usually no need to monitor the mixture as it is used. Normaladditions to replace the amounts of the liquid removed by dippingpatterns is usually sufficient to maintain the mixture in a usablecondition for extended periods of time. Another important advantage ofthe new mixture is that the colloidal refractory particles have notendency to settle so that the mixture is completely stable. This avoidsthe necessity of constantly restirring the mixture.

Other advantages and a fuller understanding of the invention will be hadfrom the following detailed description.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The process of the presentinvention involves the steps of coating disposable investment castingpatterns composed primarily of organic material with a liquidcomposition consisting of a hydrophilic agent in the form of colloidalrefractory particles dispersed in a liquid medium which is at least inpart an organic liquid capable of wetting the patterns. The patterns,which may be easily coated by dipping them into the liquid, are dried todeposit the colloidal refractory on their surfaces and thereby renderthe pattern surfaces hydrophilic. It has been found that patternstreated in the foregoing manner to render their surfaces hydrophilic arereadily wetted by the water-base refractory slurries used in theproduction of bulk investment molds and ceramic shell molds.

It is preferred to formulate the liquid pattern treating compositionusing an aqueous sol of colloidal refractory material as the hydrophilicagent and by mixing the sol with a compatible liquid medium whichcontains the organic liquid or liquids in an amount at least suffi cientto cause the mixture to wet the pattern surfaces. By compatible it ismeant that the liquid medium is sufficiently miscible with the sol toform a single phase mixture. Acid stabilized, aqueous colloidalrefractory sols are especially suitable for use because they aremiscible with the required organic liquids to form a stable mixture.Alkali stabilized sols also are usable, but they usually must beacidified prior to formulating the mixture in order to prevent theorganic liquids from gelling or precipitating the colloidal refractory.

Various aqueous sols of colloidal refractory material are availablecommercially and have been found satisfactory for use as the hydrophilicagent. Examples of the known sols are aqueous or water-base colloidalsilica sols, aqueous colloidal zirconia (ZrO sols, and aqueous colloidalaluminosilicate sols. The commercially available sols typically have acolloidal refractory content ranging from about l5 to percent by weightand a particle size ranging from about 2 to millimicrons. Such solsfunction satisfactorily for purposes of the present invention.

The aqueous sols are included in the mixture in an amount such that thecolloidal refractory content is sufficient to render the surfaces of thepattern to which the mixture is applied hydrophilic. The minimum amountof colloidal refractory should be about 0.5 percent by weight of themixture, and the preferred range of the refractory content is from 1.5percent to 5 percent by weight of the mixture. While considerably largeramounts of the refractory can be used, it has been found that arefractory content in excess of about 5 percent by weight does notproduce significant improvements in the formation of the desiredhydrophilic film on the treated patterns and is uneconomical.Furthermore, mixtures containing extremely large amounts of colloidalrefractory in relation to the or ganic liquid, for example, a mixture ofone part by volume organic liquid and parts by volume of a colloidalsilica sol having a silica content of 34 percent by weight, have certaindisadvantages. Such mixtures are slow drying which is inconvenient. Theslow drying rate combined with the excessive refractory concentrationmay make it difficult to obtain optimum uniform coverage when themixture is applied to a pattern.

The primary function of the organic liquids is to impart to the mixturethe capability of wetting the patterns so that the colloidal refractorywill be deposited substantially uniformly on their surfaces afterdrying. Accordingly, the organic liquid must have the property ofwetting the particular patterns which are to be treated. There are manydifferent pattern material blends employed in the investment castingindustry and, depending upon their composition, these blends exhibit arange of wettability characteristics, i.e., are susceptible to beingwetted by a particular organic liquid in different degrees. The usualpattern blends consist of natural and/or synthetic waxes or a blend ofsuch waxes with a natural and/or synthetic resin. Other organic patternswhich find some use are composed of synthetic resins, such aspolystyrene. It has been discovered that organic liquids having lowvalues of surface tension are capable of wetting the largest number ofthese different pattern material compositions, and that the usefulnessof organic liquids in terms of their broad applicability decreases asthe surface tension in creases. The preferred liquids have surfacetension values less than 28 dynes per centimeter measured at C., and themost preferred liquids which are useful in formulating treatingsolutions for general purpose application have a surface tension lessthan 24 dynes per centimeter at 20C.

While it is desired to employ organic liquids having as low a surfacetension possible in order to formulate a mixture which can be used towet a large number of different pattern material compositions, it is tobe understood that liquids having surface tension values greater thanthe indicated preferred minimum values can be used in particularsituations. ln the case of liquids which are not significantly morevolatile than water, the ability to wet a pattern material can be easilydetermined by dipping a piece of the material into the liquid andobserving whether the liquid withdraws or recedes from areas of thepiece when it is withdrawn from the liquid. In the case of more volatileliquids, the wetting ability is determined by treating a specimen ofpattern mate rial with a mixture formulated with the liquid, drying thespecimen, applying a water-base refractory slurry, and then observingwhether the slurry recedes from areas of the treated specimen.

In addition to the required property of being able to wet the particular.pattern material to be treated, the organic liquids which are useful informulating the mixture of this invention are at least partially solublein water, and are preferably soluble in water in all proportions. Thischaracteristic assures that the organic liquids can be mixed with theaqueous sols to form single phase mixtures with the colloidal refractorydispersed throughout. The most preferred liquids are furthercharacterized by being more volatile than water. Mixtures formulatedwith organic liquids which are more volatile than water are fast dryingand are therefore advantageous to use.

Examples of useful water soluble, organic liquids which are morevolatile than water and have surface tension values less than 24 dynesper centimeter at 20C include methyl alcohol, ethyl alcohol, isopropylalcohol, acetone and the like. Of these liquids, isopropyl alcohol isespecially preferred for a number of reasons. Mixtures based onisopropyl alcohol are particularly effective in wetting practically allof the commercially available pattern materials, and this property ismaintained over a wide concentration range. In addition, isopropylalcohol is very compatible with aqueous, acidic colloidal silica sols,is not hazardous to use, and is economical. Examples of water solubleorganic liquids which are less volatile then water but are neverthelessuseful because of their low surface tension values include n-propylalcohol, diacetone alcohol, and the like. Examples of useful organicliquids which are characterized by being partially soluble in water andby surface tension values less than 281 dynes per centimeter at 20C.include methyl acetate, methyl ethyl ketone and the like. Organicliquids, such as methyl ethyl ketone, which are capable of wetting manyof the organic pattern materials but which have limited solubility inwater or poor compatibility with the preferred acidic, aqueous colloidalrefractory sols, may be used in the presence of a small amount of athird liquid, such as isopropyl alcohol, which will make the overallcomposition compatible.

As has been indicated above, the amount of the organic liquid is atleast sufficient to cause the mixture to wet the surface of the patternsto which the mixture is applied. In most instances, the organic liquidshould be present in an amount of at least 6 percent by weight of themixture, but a much larger amount, for example, percent or more, ispreferred. An amount of the organic liquid exceeding the usable minimumis desired, since the preferred organic liquids are more volatile thanwater and therefore cause the mixture to dry faster on the patterns. Afast drying rate is advantageous, since it reduces the waiting timeafter dipping and prevents excessive drainage of the treating mixturewhich tends to cause uneven coverage. The maximum amount of the organicliquid that can be used, assuming complete compatibility with the sol,is the amount that dilutes the refractory content of the sol to theminimum amount required to render the pattern surfaces hydrophilic.

An example of an especially preferred mixture formulated in accordancewith the invention consists of the following:

93.75 parts by weight isopropyl alcohol 6.25 parts by weight of anaqueous, acidic colloidal silica sol having a pH of about 3.1, anaverage of particle size in the'range of from 16 to 22 millimicrons, andcontaining 34 percent by weight SiO and less than 0.01 percent by weightNa O.

The medium or vehicle with which the aqueous sols are mixed may includeother liquids in addition to one or more of the organic liquidsdescribed above. It is possible, for example to add a certain amount ofwater to the mixture to reduce its cost and yet maintain the usefulproperties. Water diluted mixtures are somewhat more limited in therange of pattern materials which the mixtures will wet satisfactorilyand have the further disadvantage of being slower drying than mixturesin which the medium consists entirely of one or more of the preferredorganic liquids, such as isopropyl alcohol. Normally, the only water inthe mixture is that which enters with the sol, although dilutedsolutions containing water in an amount as high as 62 percent by weighthave been used successfully in some instances.

The liquid medium also may contain a solvent for the purpose of removingexcessive amounts of lubricant from the pattern surfaces. Lubricants ofvarious types, for example, silicone fluids such as dimethyl silioxanepolymers, are commonly sprayed on the surfaces of pattern injection diesto facilitate release of the patterns. A certain amount of thislubricant may remain on the pattern surfaces after injection. When theamount of the lubricant is not excessive, no particular problems areencountered, but on some occasions the pattern may have such a heavylayer of lubricant that the preferred compositions of the invention willnot wet the patterns satisfactorily. In such cases, a solvent for thelubricant can be added to the pattern coating mixture. The solvent usedfor this purpose should not be one which will dissolve the pattern,since such solvents can cause loss of pattern detail and can cause therefractory particles to be covered with a layer of the wax or otherpattern material so as to prevent the mixture from functioning in itsintended manner. Suitable solvents for use in the mixture include 1, l,l-trichloroethane and the like.

The liquid compositions of this invention can be applied to patterns inany expeditious manner. For example, the patterns can be dipped into aquantity of the liquid and then allowed to dry, whereby the colloidalrefractory is deposited over the pattern surfaces. The dipping time isnot critical, although it will be understood that the pattern should notbe immersed and withdrawn so fast that the liquid does not have a chanceto displace the air film around the pattern.

The invention is further illustrated by the following examples:

Example I Silica Sol lsopropyl Alcohol (Parts by Volume) (Parts byVolume) -Continued Silica Sol lsopropyl Alcohol (Parts by Volume) (Partsby Volume) 1 l5 1 20 l 25 l 40 Specimens of commercially availabledental wax were dipped in each mixture and were allowed to dry. Anotherspecimen of the same dental wax was dipped in straight isopropyl alcoholand allowed to dry. Each of the treated specimens was then dipped indistilled water and one additional specimen which had no treatment wasalso dipped in distilled water. The water wetted each of the specimenstreated with the silica sol/isopropylalcohol mixtures and formed a thinfilm over the surfaces. It was found that the water did not wet theuntreated specimen and the specimen which had been dipped in straightisopropyl alcohol. In the latter two instances, the water formed beadson the wax surfaces.

The specimens were then dried and dipped in a refractory slurryconsisting essentially of 15% pounds of refractory material and 5 poundsof an alkaline, aqueous colloidal silica sol. The refractory materialused in the slurry was composed of percent zircon powder and 40 percentfused silica powder. The silica sol had a pH of 9.7, an approximateparticle diameter of 7 millimicrons, and contained 30 percent by weightSiO and approximately 0.43 percent by weight Na O.

All of the wax specimens which had been treated with the silicasol/isopropyl alcohol mixtures were wetted and coated by the slurry. Thecoverage of the specimen which had been dipped in straight isopropylalcohol was incomplete and large areas were bare. The untreated specimenevidenced no substantial wetting so that almost the entire surfaces werebare.

The foregoing tests demonstrate that the liquid mixtures of acidiccolloidal silica sol and isopropyl alcohol are effective over a widerange of composition. The tests further demonstrate that the wetting bythe slurry is a result of the silica which is deposited on the patternsurfaces by drying of the coating mixtures, since merely dipping thespecimens in isopropyl alcohol was not effective. It is also shown thatthe mixtures prepared according to the invention are effective to causeuniform coverage of organic pattern materials by refractory slurrieseven though the conventionally used wetting agents are omitted entirelyfrom the slurries.

Example ll Wax patterns were injected in dies that had been heavilylubricated with a 350 centistokes silicone fluid. It was found thatisopropyl alcohol would not completely wet these patterns because of thepresence of the lubricant on their surfaces.

A pattern treating mixture was then following composition:

3 parts by volume l,l,l-trichloroethane,

7 parts by volume isopropyl alcohol,

1 part by volume of an alcohol water-base, acidic colloidal silica solhaving a pH of 3.5 i 0.5, an average particle diameter in the range offrom 16 to 25 millimicrons, and containing in amounts by weight 28percent SiO 32 percent water, 40 percent alcohol, and less than 0.005percent Na O.

prepared of the One of the patterns was dipped for 30 seconds in theforegoing mixture, dried, and then dipped in a slurry consisting of 6pounds, 12 ounces of refractory material and 2 pounds, ounces of analkaline stabilized, aqueous colloidal silica sol. The refractorymaterial used in the slurry was composed of 60 percent zircon powder and40 percent fused silica powder. The silica sol had a pH of 8.6, anaverage particle size in the range of from 16 to 22 millimicrons, andcontained in amounts by weight 35 percent SiO and 0.10 percent Na O.

The pattern to which the treating mixture had been applied was coatedsatisfactorily by the slurry. Another pattern was treated simply with atrichloroethylene/isopropyl alcohol solution and was dipped into thesame slurry. The latter pattern was wetted very poorly by the dipcoatslurry and an incomplete coating was obtained.

Example III A liquid, pattern coating mixture was prepared according tothe invention using an alkali stabilized colloidal silica sol. The solwas an alkaline, aqueous, fine particle size sol having a pH of about9.7, an approximate particle diameter of 7 millimicrons, and consistedof about 30 percent by weight SiO and about 0.43 percent by weight Na O.The sol was acidified and mixed with isopropyl alcohol, according to thefollowing formula:

2 parts by volume sulfuric acid 100 parts by volume silica so! 1000parts by volume isopropyl alcohol The acid was added to the sol withrapid stirring to avoid localized gelling or precipitation of thesilica, and the solution was then added to the isopropyl alcohol. Waxpatterns were coated with the resulting mixture and the treated patternswere satisfactorily wetted with a water-base slurry of the typedescribed in the previous examples. It was found that the mixtureformulated with alkali stabilized silica sol was still usable afterstoring in a closed container for a period of three weeks.

Example IV Patterns were injection molded from the composition ofExample I of US. Pat. No. 3,296,006. One pattern was dipped for secondsin straight methyl alcohol and another pattern was dipped for 15 secondsin a coating mixture containing 100 parts by volume methyl alcohol and10 parts by volume of the same aqueous,

I acidic colloidal silica so] used in preparing the coating mixtures ofExample I.

After drying the treated patterns together with a pattern which wasgiven no treatment were dipped in a slurry prepared as described inExample II. The slurry readily wetted and coated the patterns which hadbeen dipped in the silica sol-methyl alcohol treating mixture. The sameslurry did not satisfactorily coat either the patterns treated withstraight methyl alcohol or the pattern which had been given notreatment.

Example V Specimens were cut from pattern wax to reveal all freshsurfaces. One specimen was dipped for 5 seconds in straight diacetonealcohol and another was dipped for 5 seconds in a liquid mixtureincluding I00 parts by volume diacetone alcohol and 10 parts by volumeof the same acidic colloidal silica sol used in the coating mixtureformulations of Example I.

The specimens were dried and were then dipped in a dipcoat slurryconsisting of refractory material and the same aqueous colloidal silicasol'used in formulating the coating mixture. The slurry composition wasas follows:

2 pounds, 12 ounces colloidal silica sol 7 pounds refractory materialconsisting of 60 percent zircon powder and 40 percent fused silicapowder The specimens treated in the silica sol/diacetone alcohol mixturewere wetted and coated satisfactorily by the dipcoat slurry. Thespecimen which had been treated only with diacetone alcohol was onlypartially wetted by the slurry and the slurry coating wasunsatisfactory.

Example VI Specimens were cut from pattern wax to reveal all freshsurfaces. One specimen was dipped for IS seconds in straight acetone anda second specimen was dipped for 15 seconds in a pattern treatingmixture containing parts by volume acetone and 10 parts by volume of theaqueous colloidal silica sol used in formulating the coating mixtures ofExample I.

After drying both specimens were dipped in the slurry of Example V. Thespecimen which had been dipped in the pattern treating mixture waswetted and coated perfectly by the slurry. The specimen which had beentreated only with acetone was wetted poorly by the slurry and largeareas of the wax surfaces were left uncoated.

Example VIII A pattern wax specimen was dipped in a treating mixturecontaining 100 parts by volume denatured ethyl alcohol and 20 parts byvolume of the aqueous colloidal silica sol used in formulating thecoating mixtures of Example I. A second specimen of the same wax wasdipped in straight denatured ethyl alcohol.

Both specimens were dried and dipped in distilled water. The specimentreated with the silica sol/- denatured ethyl alcohol mixture was wettedcompletely by the water. The other specimen which had been dipped instraight denatured alcohol was wetted poorly and the water film recededto leave areas of the specimen bare.

Example IX A pattern treating mixture was prepared by first mixing 1.5parts by volume of isopropyl alcohol with one part by volume of theaqueous colloidal silica sol used in formulating the mixtures of ExampleI. The resulting mixture was added to 15 parts by volume of methyl ethylketone to obtain a single phase mixture. In the absence of isopropylalcohol, methyl ethyl ketone was found to be incompatible with the sol.When the sol was added to methyl ethyl ketone in quantities of 1:10parts by volume of 1:20 parts by volume, the combinations were notcompletely miscible and two phases resulted in each instance.

Specimens were cut from pattern material wax to reveal all freshsurfaces. One specimen was dipped for 5 seconds in straight methyl ethylketone and a second specimen was dipped for 5 seconds in the abovepattern mixture containing methyl ethyl ketone, silica sol and isopropylalcohol. The patterns were dried and were then dipped in the dipcoatslurry used in Example V. The slurry wetted and coated the specimenwhich had been dipped in the pattern treating mixture. The slurry didnot wet the specimen which had been dipped in straight methyl ethylketone.

Example X Specimens of a pattern material wax were treated with amixture consisting of one part by volume isopropyl alcohol and parts byvolume of the same colloidal silica sol used in formulating the coatingmixtures of Example I. The specimens were wetted satisfactorily by themixture and, after drying, were wetted and coated satisfactorily by adipcoat slurry of the type described in Example 1. Although thedescribed treating mixture was found satisfactory for use, mixturesprepared using a large amount of silica so] in relation to the organicliquid are not preferred for the reasons previously discussed. Suchmixtures are expensive because of the large amount of colloidal silicasol and have certain disadvantages, including a slower drying rate andthe difficulty of obtaining uniform coverage due to the excessive silicaconcentration.

Example XI Specimens of pattern wax were dipped in a treating mixtureconsisting of 2 parts by volume of the same colloidal silica sol used informulating the mixtures of Example l, 10 parts by volume water andparts by volume isopropyl alcohol. The mixture wetted the patterns and,after drying, the treated patterns were satisfactorily coated with adipcoat slurry. As explained above, mixtures as used in this examplewhich have been diluted with water are somewhat limited in the patternmaterials which they will wet and also have the disadvantage of beingslower drying relative to the mixtures in which the medium consistsentirely of the required organic liquid, such as isopropyl alcohol.

Example Xll A liquid mixture was prepared using an aqueous colloidalzirconia sol containing about 20.69 percent by weight ZrO and having anestimated particle size of from 5 to millimicrons and a pH in the rangeof from 0.5 to L0. The sol was mixed with isopropyl alcohol in an amountof 10 parts by volume colloidal zirconia sol to 50 parts by volumeisopropyl alcohol. A specimen of the same wax used in Example I wastreated with the solution and dried. A second specimen was treated withisopropyl alcohol and dried, and a third specimen was untreated. Allthree specimens were dipped in distilled water and it was found that thewater completely wetted the specimen treated with colloidal zirconia Theother two specimens were not wetted by the water.

Example Xlll A liquid treating composition was prepared using an aqueouscolloidal aluminosilicate sol containing about percent by weight solidsand having a pH in the range of from 4.0 to 4.6. The average particlesize diameter was estimated to be 16 millimicrons. One part by volumeHCl was added to 10 parts by volume of the sol to prevent precipitationof the solids, and the mixture was added while stirring to 89 parts byvolume isopropyl alcohol. A wax specimen treated with this compositionwas wetted satisfactorily by distilled water. An

untreated specimen of the same wax and another specimen treated onlywith isopropyl alcohol were not wetted by distilled water.

Example XIV A liquid treating composition was prepared by mixing 26parts by volume methyl acetate with parts by volume of the acidstabilized silica sol used in the mixtures of Example I. A wax specimentreated with this composition was wetted by distilled water, while anuntreated specimen of the same wax was not wetted by the water.

Many modifications and variations'of the invention will be apparent tothose skilled in the art in the light of the foregoing detaileddisclosure. Therefore, it is to be understood that, within the scope ofthe appended claims, the invention can be practiced otherwise than asspecifically described.

What is claimed is:

1. A process of preparing a disposable casting pattern composedprimarily of organic material for use in the production of an investmentmold made with a waterbase refractory slurry, said process being carriedout prior to the formation of the investment mold and comprising thesteps of: v

a. coating the pattern with a liquid mixture consisting essentially ofdiscrete, individual, colloidal refractory particles in a liquid mediumcomprised of at least one organic liquid characterized by the capabilityof wetting the pattern,

the colloidal refractory being present in an amount of at least about0.5 percent by weight of the mixture and the organic liquid beingpresent in an amount sufficient to cause the mixture to wet the pattern,and

b. drying the coated pattern to deposit the colloidal refractoryparticles on the pattern surfaces in order to render the patternsurfaces hydrophilic and thereby promote uniform surface coverage by asubsequently applied water-base refractory slurry.

2. A method as claimed in claim 1 in which the organic liquid ischaracterized by a surface tension less than 28 dynes per centimeter at20C.

3. A method as claimed in claim 1 in which the organic liquid is presentin an amount of at least 6 percent by weight of the mixture.

4. A process of preparing a disposable casting pattern composedprimarily of organic material for use in the production of an investmentmold made with a waterbase refractory slurry, said process being carriedout prior to the formation of the investment mold and comprising thesteps of:

a. coating the pattern with a liquid consisting essentially of awater-base sol containing discrete, individual colloidal refractoryparticles admixed with a liquid medium comprised of at least one organicliquid characterized by the capability of wetting the pattern, thecolloidal refractory content of the mixture being at least 0.5 percentby weight and the organic liquid being present in an amount to cause themixture to wet the pattern, and

b. drying the coated pattern to deposit the colloidal refractory on thepattern surfaces in order to render the pattern surfaces hydrophilic andthereby promote uniform surface coverage by a subsequently appliedwater-base refractory slurry.

5. A method as claimed in claim 4} in which the sol is acidic.

6. A method as claimed in claim 4 in which the organic liquid has asurface tension of less than 28 dynes per centimeter at 20C.

7. A method as claimed in claim 1 in which the organic liquid is presentin an amount of at least 6 percent by weight of the mixture.

8. A method as claimed in claim 4 in which the colloidal refractorycontent of the mixture is in the range of from 1.5 to 5 percent byweight of the mixture.

9. A process of preparing a disposable casting pattern composedprimarily of organic material for use in the production of an investmentmold made with a waterbase refractory slurry, said process being carriedout prior to the formation of the investment mold and comprising thesteps of:

a. coating the pattern with a liquid mixture consisting essentially ofan acidic, water-base sol containing discrete, individual, colloidalrefractory particles and a liquid medium containing at least one organicliquid characterized by the capability of wetting the pattern and by asurface tension of less than 28 dynes per centimeter at 20C. thecolloidal refractory content of the mixture being at least 0.5 percentby weight and the organic liquid being present in an amount of at least6 percent by weight of the mixture, and

b. drying the coated pattern to deposit the colloidal refractory on thepattern surfaces in order to render the pattern surfaces hydrophilic andthereby promote uniform surface coverage by a subsequently appliedwater-base refractory slurry.

10. A method as claimed in claim 9 in which the colloidal refractorycontent is in the range of from 1.5 to 5 percent by weight of themixture.

111. A method as claimed in claim 9 in which the organic liquid ispresent in an amount of at least 90 percent by weight of the mixture.

l2. A process of preparing a disposable casting pattern composedprimarily of organic material for use in the production of an investmentmold made with a water-base refractory slurry, said process beingcarried out prior to the formation of the investment mold and comprisingthe steps of:

a. coating the pattern with a liquid mixture consisting essentially ofan acidic, water-base sol containing discrete, individual, colloidalrefractory particles and a liquid medium containing at least one organicliquid characterized by the capability of wetting the pattern and by asurface tension of less than 28 dynes per centimeter at 20C. thecolloidal refractory content of the liquid mixture being in the range offrom 1.5 to 5 percent by weight of the mixture, and the organic liquidbeing present in an amount of at least about 90 percent by weight of themixture, and

b. drying the coated pattern to deposit the colloidal refractory on thepattern surfaces to render the pattern surfaces hydrophilic and therebypromote uniform surface coverage by a subsquently applied 5 water-baserefractory slurry.

13. A process of preparing a disposable casting pattern composedprimarily of organic material for use in the production of an investmentmold made with a water-base refractory slurry, said process beingcarried out prior to the formation of the investment mold and comprisingthe steps of:

a. coating the pattern with a liquid mixture consisting essentially of:

discrete, individual, colloidal particles of at least one refractoryselected from the class consisting of silicic and zirconic materials,said particles having a size of from about 2 to 70 millimicrons, and

a liquid medium comprised of at least one organic liquid having thecapability of wetting the pattern and selected from the class consistingof alcohols, ketones and esters, and

b. drying the coated pattern to deposit the colloidal refractoryparticles on the pattern surfaces in order to render the patternsurfaces hydrophilic and thereby promote uniform surface coverage bysubsequently applied water-base refractory slurry.

14 A process of preparing a disposable casting pattern composedprimarily of organic material for use in the production of an investmentmold made with a water-base refractory slurry, said process beingcarried out prior to the formation of the investment mold and comprisingthe steps of:

a. coating the pattern with a liquid mixture consisting essentially of:

an acidic, water-base sol containing discrete, individual, colloidalparticles of at least one refractory selected from the class consistingof silicic and zirconic materials, said particles having a size fromabout 2 to 70 millimicrons, and

a liquid medium comprised of at least one organic liquid selected fromthe class consisting of alcohols, ketones and esters and characterizedby the capability of wetting the pattern and by a surface tension ofless than 28 dynes per centimeter at 20C. and

b. drying the coated pattern to deposit the colloidal refractoryparticles on the pattern surfaces to render the pattern surfaceshydrophilic and thereby promote uniform surface coverage by subsequentlyapplied water-base refractory slurry.

15. A method as claimed in claim 14- in which the col loidal refractorycontent of the liquid mixture is in the range of from about 1.5 topercent by weight of the total weight of the mixture, and in which theorganic liquid is present in a minimum amount of about 90 percent byweight of the total weight of the mixture.

2. A method as claimed in claim 1 in which the organic liquid ischaracterized by a surface tension less than 28 dynes per centimeter at20*C.
 3. A method as claimed in claim 1 in which the organic liquid ispresent in an amount of at least 6 percent by weight of the mixture. 4.A process of preparing a disposable casting pattern composed primarilyof organic material for use in the production of an investment mold madewith a water-base refractory slurry, said process being carried outprior to the formation of the investment mold and comprising the stepsof: a. coating the pattern with a liquid consisting essentially of awater-base sol containing discrete, individual colloidal refractoryparticles admixed with a liquid medium comprised of at least one organicliquid characterized by the capability of wetting the pattern, thecolloidal refractory content of the mixture being at least 0.5 percentby weight and the organic liquid being present in an amount to cause themixture to wet the pattern, and b. drying the coated pattern to depositthe colloidal refractory on the pattern surfaces in order to render thepattern surfaces hydrophilic and thereby promote uniform surfacecoverage by a subsequently applied water-base refractory slurry.
 5. Amethod as claimed in claim 4 in which the sol is acidic.
 6. A method asclaimed in claim 4 in which the organic liquid has a surface tension ofless than 28 dynes per centimeter at 20*C.
 7. A method as claimed inclaim 4 in which the organic liquid is present in an amount of at least6 percent by weight of the mixture.
 8. A method as claimed in claim 4 inwhich the colloidal refractory content of the mixture is in the range offrom 1.5 to 5 percent by weight of the mixture.
 9. A process ofpreparing a disposable casting pattern composed primarily of organicmaterial for use in the production of an investment mold made with awater-base refractory slurry, said process being carried out prior tothe formation of the investment mold and comprising the steps of: a.coating the pattern with a liquid mixture consisting essentially of anacidic, water-base sol containing discrete, individual, colloidalrefractory particles and a liquid medium containing at least one organicliquid characterized by the capability of wetting the pattern and by asurface tension of less than 28 dynes per centimeter at 20*C. thecolloidal refractory content of the mixture being at least 0.5 percentby weight and the organic liquid being present in an amount of at least6 percent by weight of the mixture, and b. drying the coated pattern todeposit the colloidal refractory on the pattern surfaces in order torender the pattern surfaces hydrophilic and thereby promote uniformsurface coverage by a subsequently applied water-base refractory slurry.10. A method as claimed in claim 9 in which the colloidal refractorycontent is in the range of from 1.5 to 5 percent by weight of themixture.
 11. A method as claimed in claim 9 in which the organic liquidis present in an amount of at least 90 percent by weight of the mixture.12. A process of preparing a disposable casting pattern composedprimarily of organic material for use in the production of an investmentmold made with a water-base refractory slurry, said process beingcarried out prior to the formation of the investment mold and comprisingthe steps of: a. coating the pattern with a liquid mixture consistingessentially of an acidic, water-base sol containing discrete,individual, colloidal refractory particles and a liquid mediumcontaining at least one organic liquid characterized by the capabilityof wetting the pattern and by a surface tension of less than 28 dynesper centimeter at 20*C. the colloidal refractory content of the liquidmixture being in the range of from 1.5 to 5 percent by weight of themixture, and the organic liquid being present in an amount of at leastabout 90 percent by weight of the mixture, and b. drying the coatedpattern to deposit the colloidal refractory on the pattern surfaces torender the pattern surfaces hydrophilic and thereby promote uniformsurface coverage by a subsquently applied water-base refractory slurry.13. A process of preparing a disposable casting pattern composedprimarily of organic material for use in the production of an investmentmold made with a water-base refractory slurry, said process beingcarried out prior to the formation of the investment mold and comprisingthe steps of: a. coating the pattern with a liquid mixture consistingessentially of: discrete, individual, colloidal particles of at leastone refractory selected from the class consisting of silicic andzirconic materials, said particles having a size of from about 2 to 70millimicrons, and a liquid medium comprised of at least one organicliquid having the capability of wetting the pattern and selected fromthe class consisting of alcohols, ketones and esters, and b. drying thecoated pattern to deposit the colloidal refractory particles on thepattern surfaces in order to render the pattern surfaces hydrophilic andthereby promote uniform surface coverage by subsequently appliedwater-base refractory slurry.
 14. A process of preparing a disposablecasting pattern composed primarily of organic material for use in theproduction of an investment mold made with a water-base refractoryslurry, said process being carried out prior to the formation of theinvestment mold and comprising the steps of: a. coating the pattern witha liquid mixture consisting essentially of: an acidic, water-base solcontaining discrete, individual, colloidal particles of at least onerefractory selected from the class consisting of silicic and zirconicmaterials, said particles having a size from about 2 to 70 millimicrons,and a liquid medium comprised of at least one organic liquid selectedfrom the class consisting of alcohols, ketones and esters andcharacterized by the capability of wetting the pattern and by a surfacetension of less than 28 dynes per centimeter at 20*C. and b. drying thecoated pattern to deposit the colloidal refractory particles on thepattern surfaces to render the pattern surfaces hydrophilic and therebypromote uniform surface coverage by subsequently applied water-baserefractory slurry.
 15. A method as claimed in claim 14 in which thecolloidal refractory content of the liquid mixture is in the range offrom about 1.5 to 5 percent by weight of the total weight of themixture, and in which the organic liquid is present in a minimum amountof about 90 percent by weight of the total weight of the mixture.